1. Field of the Invention
This invention relates to a tilt cylinder apparatus for use in an outboard motor or the like.
2 . Discussion of the Background Art
The tilt cylinder apparatus for use with a boat propeller unit, for example, an outboard motor, is disposed between the boat body and an outboard motor tiltingly supported by the boat body, and is used for tilting the outboard motor by extending the cylinder apparatus.
The aforementioned tilt cylinder apparatus for boat propeller has been disclosed in U.S. Pat. No. 3,990,660 (first prior art reference) and Japanese Patent Application publication (JP-B) No.2-58155 (second prior art reference).
The first prior art will be described in detail. An interior of the cylinder is sectioned to a rod side chamber containing a piston rod and a piston side chamber not containing the piston rod, by means of a piston. An air chamber is provided in the piston side chamber of the cylinder across a free piston. The rod side chamber communicates with the piston side chamber through a communicating path formed in the piston. A selecting valve for selecting an opening/closing of this communicating path is disposed in this piston. A function of tilting up the propeller unit is executed by opening the selecting valve by operating an operating rod provided in the piston rod so as to ensure communication between the piston side chamber and the rod side chamber through the communicating path, and move the piston to the rod side chamber by an action of air pressure in the air chamber so as to push the piston rod out of the cylinder.
According to the second prior art reference, the interior of the cylinder is sectioned to the rod side chamber and the piston side chamber by the piston. The air chamber is provided in the piston side chamber of the cylinder. A communicating path between the rod side chamber and the piston side chamber is opened or closed by means of the selecting valve. The communicating path and the selecting valve are provided outside the cylinder. The aforementioned function of tilting up the propeller unit is executed by opening the communicating path by operating the selecting valve so that the piston is moved to the rod side chamber by action of air pressure in the air chamber, thereby pushing the piston rod out of the cylinder.
According to the first prior art reference, the air chamber is provided in the cylinder and the communicating path and the selecting valve are disposed in the piston. As a result, a compactness of the apparatus is achieved. However, because the operating rod for operating the selecting valve is disposed within the piston rod and an operating portion of the operating rod is located at an end of the piston rod so that the operating rod is apart from the boat body, the operability of the selecting valve, that is, the operability of the apparatus is reduced.
According to the second prior art reference, because the communicating path and the selecting valve are disposed outside the cylinder, a position of the operating portion of the selecting valve can be determined arbitrarily. However, because the communicating path and the selecting valve are disposed outside the cylinder, enlargement of the apparatus is unavoidable.